1. First, go to dashboard > posts. Then select the posts that fit in to a category. (example: I am selecting posts based on photography.)
2. Once you've selected the posts, click the label icon above the posts and then click 'new label.' Then click ok.
The next bit is pretty easy. All you need to do, is go to your blog, and click on the labels you want and copy their url's into a word document. Then you can link them up to your sidebar, or image-map. So when you click on a certain link it will show you all the posts in that category. Sorry if it's a bit confusing!
If you like, you can delete the 'label's widget from your footer as you won't need it anymore.
I hope this is helpful and if you guys have any questions or need help just leave a comment! :)